Medicare Supplement

Plan A to N: How Medigap's Letter System Works

NORTH BRUNSWICK, N.J. — If you've ever tried to compare Medicare Supplement policies and felt like you were reading an eye chart, you're not alone. Medigap plans are sold under single-letter names — A, B, C, D, F, G, K, L, M and N — and the letters aren't a grade. They're a shorthand for a benefits package that the federal government has standardized, so every insurer selling "Plan G," for example, has to cover the same core things.

Understanding the standardized Medigap plan letters

Here in North Brunswick, which sits in Middlesex County, retirees comparing Original Medicare with a Medigap policy are working from the same standardized menu as retirees anywhere else in most of the country. That's the point of the letters: to make apples-to-apples comparison possible.

What Medigap actually does

Medigap is a private insurance policy you buy to fill in the "gaps" left by Original Medicare. Original Medicare (Part A hospital and Part B medical) pays a big share of covered services, but not all of it. You still owe deductibles, coinsurance and copays, and there's no yearly out-of-pocket limit on Original Medicare by itself.

A Medigap policy can pick up some or all of those leftover costs, depending on the letter you choose. It only works with Original Medicare — you cannot use a Medigap policy with a Medicare Advantage plan.

Why the letters exist

Before standardization, Medigap policies were a confusing mix, and it was almost impossible to compare one company's product to another's. Federal law changed that. Today, if you look at Plan G from Company A and Plan G from Company B, the covered benefits are identical. The price and the customer service can differ, but the benefits inside the letter cannot.

That standardization is why Medicare's own guides list the letters in a grid — it's meant to be a checklist, not a marketing pitch.

What each letter generally covers

Every Medigap plan covers, at minimum, Part A coinsurance and hospital costs for an extra year after Medicare benefits are used up, plus some Part B coinsurance and the first three pints of blood each year. From there, coverage builds:

• Plans A and B cover the basics.
• Plans D, G, M and N cover more, including skilled nursing coinsurance and foreign travel emergency care in most cases. Plan N has small copays for some office and ER visits.
• Plans K and L are cost-sharing plans — they pay a percentage until you hit an out-of-pocket limit for the year.
• Plans C and F were the most comprehensive, but they're closed to people who became Medicare-eligible on or after January 1, 2020. If you were eligible before that date and never enrolled, you may still be able to buy one.

For the full grid of what each letter covers, Medicare.gov keeps the official comparison chart.

What Medigap does not do

Medigap does not include prescription drug coverage. To get drug coverage, you'd enroll separately in a Part D plan. In 2026, Part D has a $2,100 annual out-of-pocket cap on covered drugs and a maximum deductible of $615. The old "donut hole" coverage gap was eliminated in 2025, and there's now an optional Medicare Prescription Payment Plan that lets you spread your drug costs across the calendar year.

Medigap also generally does not cover dental, vision, hearing aids or long-term custodial care.

Timing matters more than most people realize

The best time to buy a Medigap policy is during your six-month Medigap Open Enrollment Period, which starts the month you're 65 or older AND enrolled in Part B. During that window, insurers cannot turn you down or charge you more because of your health.

Outside that window, in most states — New Jersey included — insurers can use medical underwriting. That means switching Medigap letters later in life is not always simple, even though the letters themselves are standardized.

Note: Medigap's enrollment window is separate from Medicare's Annual Enrollment Period (October 15 – December 7) and the Medicare Advantage Open Enrollment Period (January 1 – March 31), which apply to different types of coverage.